Spear guns are well known devices used by underwater swimmers and scuba divers to kill fish. There are larger fish, such as sharks, which may be encountered, and which are not easily killed by a spear. Because of the danger to the diver, there has been a need for a more potent weapon for defense against sharks. Available in the market today are devices to be screwed onto the forward end of a spear shaft in place of the pointed tip. The devices include a receiver to be loaded with a cartridge blank or a bullet, and a spring biased firing gun which moves forward by inertia when the spear hits the fish and strikes the percussion cap of the cartridge firing the head. The problems with this arrangement is that it is time consuming to remove a spear point and attach the prior art cartridge device. There may not be sufficient time to do this before the shark attacks. Furthermore, the firing pin mechanism and explosive charge are subject to corrosion and contamination by sea water under pressure by submersion by a diver, and may not function properly when needed.
It is an object of this invention to provide an improved expendable explosive head for a spear. It is another object of this invention to provide such a head that is substantially corrosion-proof and waterproof under normal diving circumstances that can be attached by merely placing it over a spear with a pointed tip without further operations. Still other objects will become apparent from the more detailed description which follows.